Aerosol dispensing containers have found widespread use in the packaging of fluid materials including a variety of both liquid and powdered particulate products. Such containers are provided with a valve-controlled discharge orifice and operate by the action of a volatile propellant which is confined within the container together with the product to be dispensed. Because the propellant has an appreciable vapor pressure at room temperature, the product in the closed container is maintained under superatmospheric pressure.
A typical aerosol unit comprises a hollow cylindrical container which is tightly closed at one end and is provided with an opening at its opposite end for receiving a dispensing valve assembly. A closure, commonly referred to as a mounting cup, serves as the closure for the container and as a support for the valve assembly. Typically, the mounting cup comprises a pedestal portion for mounting the valve unit, a panel portion extending from the pedestal portion, a skirt portion depending from the periphery of the panel, and an annular channel portion extending outwardly from the skirt. When the mounting cup is placed in sealing position on the container, the channel is positioned over the bead surrounding the container opening and the lower portion of the skirt adjacent to the channel is flared or clinched outwardly against the underside of the bead. To ensure adequate sealing between the closure and the container, the cup is provided with a gasket in the channel, or predominantly in the channel, of the cup.
In U.S. Pat. Nos. 4,546,525 ("the 525 patent") and 4,547,948 ("the 948 patent"), a novel gasketed mounting cup system, including novel method and apparatus, is described wherein the gasket material is disposed on the mounting cup in the preferred position for effecting a seal between the mounting cup and the bead of the container, in an exceptionally rapid and efficient manner to form gasketed-mounting cups having excellent sealing characteristics. In general, the method of invention of the '525 and '948 patents comprises passing a tubular sleeve of gasket material onto a compressible mandrel; initially positioning and aligning the skirt of the mounting cup and the contiguous end of the mandrel such that the sleeve of gasket material may pass onto the skirt, said mandrel having fixed and moveable portions with respect to each other and to their movement toward and away from the mounting cup; urging the moveable portion of the gasket material bearing mandrel toward the mounting cup such that the gasket material passes onto the skirt of the cup; causing the moveable portion of the mandrel to retract to its initial position, cutting the sleeve at a point between the mounting cup and the mandrel to leave a band of gasket material; and subsequently, advancing the mounting cup to a station whereat the band of the gasket material is urged further onto the skirt of the mounting cup, whereby the band of gasket material does not extend beyond the skirt of the mounting cup. Subsequently, the gasket is advanced to the ultimately desired position partially within the channel of the mounting cup. The '525 and '948 patents are incorporated by reference herein.
In the United States, aerosol containers are typically filled by the undercap filling method. First, the product to be dispensed is deposited into the container. Then a mounting cup, including the valve and dip tube, is placed on the container such that the bead of the container is within the channel of the mounting cup. The filling head of an undercap filling machine then encompasses the top of the container, creating an airtight seal. Air is then evacuated from the container. The suction created during evacuation raises the mounting cup off of the container bead. Propellant is then forced into the container opening beneath the mounting cup and the mounting cup is repositioned and clinched to the container bead. In certain applications, the propellant can be dissolved in the product, mixed and inserted into the container in one step. Product saturated carbon dioxide is one common example.
During the filling process, suction during evacuation or the force of the propellant during filling can displace the gasket from its position within the channel of the mounting cup, preventing a proper seal on clinching. In some cases, the gasket can be completely displaced by the propellant filling the container, forcing the gasket into the container. This is referred to as a "blown" gasket.
The dip tube of the container is usually slightly longer than the height of the container to insure that its end is positioned at the bottom of the container. As shown in FIG. 1, when the mounting cup is positioned on the container bead, the dip tube is slightly bent. This can provide an upward force which can displace the mounting cup from the container bead, interfering with proper clinching. To ensure that the mounting cup is maintained on the container bead prior to clinching, protrusions are created around the skirt of the mounting cup which are below the container bead when the mounting cup is in position. Such protrusions 14a are also shown in FIG. 1. The force provided by the bent dip tube is generally insufficient to overcome the retaining force provided by the protrusions. The protrusions are formed by a tool placed around the pedestal of the mounting cup, which forces out particular sections of the skirt of the cup.
Such protrusions can scratch the container bead or walls of the opening of the container when the mounting cup is being positioned, promoting corrosion. In addition, the mounting cup can be split or punctured during formation of the protrusion.